C#: Introduce Ssa::Definition::getElement() and AssignableDefinition::getElement()

Author: hvitved

csharp/ql/src/semmle/code/csharp/Assignable.qll

@@ -484,6 +484,12 @@ class AssignableDefinition extends TAssignableDefinition {
    */
   Expr getExpr() { none() }
 
+  /**
+   * Gets the underlying element associated with this definition. This is either
+   * an expression or a parameter.
+   */
+  Element getElement() { result = this.getExpr() }
+
   /** DEPRECATED: Use `getAControlFlowNode()` instead. */
   deprecated
   ControlFlow::Node getControlFlowNode() { result = this.getAControlFlowNode() }
@@ -800,6 +806,8 @@ module AssignableDefinitions {
       result = p.getCallable().getEntryPoint()
     }
 
+    override Parameter getElement() { result = p }
+
     override Callable getEnclosingCallable() {
       result = p.getCallable()
     }

csharp/ql/src/semmle/code/csharp/dataflow/Nullness.qll

@@ -163,9 +163,9 @@ private predicate defMaybeNull(Ssa::Definition def, string msg, Element reason)
     de = def.getARead() |
     reason = de.getANullCheck(_, true) and
     msg = "as suggested by $@ null check" and
-    not def instanceof Ssa::PseudoDefinition and
-    strictcount(Location l |
-      l = any(Ssa::Definition def0 | de = def0.getARead()).getLocation()
+    not de = any(Ssa::PseudoDefinition pdef).getARead() and
+    strictcount(Element e |
+      e = any(Ssa::Definition def0 | de = def0.getARead()).getElement()
     ) = 1 and
     not nonNullDef(def) and
     // Don't use a check as reason if there is a `null` assignment

csharp/ql/src/semmle/code/csharp/dataflow/SSA.qll

@@ -2252,6 +2252,18 @@ module Ssa {
     /** Gets the basic block to which this SSA definition belongs. */
     BasicBlock getBasicBlock() { this.definesAt(result, _) }
 
+    /**
+     * Gets the syntax element associated with this SSA definition, if any.
+     * This is either an expression, for example `x = 0`, a parameter, or a
+     * callable. Pseudo nodes have no associated syntax element.
+     */
+    Element getElement() {
+      exists(BasicBlock bb, int i |
+        this.definesAt(bb, i) |
+        result = bb.getNode(i).getElement()
+      )
+    }
+
     /**
      * Holds if this SSA definition assigns to `out`/`ref` parameter `p`, and the
      * parameter may remain unchanged throughout the rest of the enclosing callable.
@@ -2341,6 +2353,8 @@ module Ssa {
       isCapturedVariableDefinitionFlowOut(this, cdef)
     }
 
+    override Element getElement() { result = ad.getElement() }
+
     override string toString() {
       if this.getADefinition() instanceof AssignableDefinitions::ImplicitParameterDefinition then
         result = getToStringPrefix(this) + "SSA param(" + this.getSourceVariable() + ")"
@@ -2384,6 +2398,8 @@ module Ssa {
       )
     }
 
+    override Callable getElement() { result = this.getCallable() }
+
     override string toString() {
       if this.getSourceVariable().getAssignable() instanceof LocalScopeVariable then
         result = getToStringPrefix(this) + "SSA capture def(" + this.getSourceVariable() + ")"